Asynapsis and unreduced gamete formation in a Trifolium interspecific hybrid

Background Unreduced gametes, a driving force in the widespread polyploidization and speciation of flowering plants, occur relatively frequently in interspecific or intergeneric hybrids. Studies of the mechanisms leading to 2n gamete formation, mainly in the wheat tribe Triticeae have shown that unreductional meiosis is often associated with chromosome asynapsis during the first meiotic division. The present study explored the mechanisms of meiotic nonreduction leading to functional unreduced gametes in an interspecific Trifolium (clover) hybrid with three sub-genomes from T. ambiguum and one sub-genome from T. occidentale. Results Unreductional meiosis leading to 2n gametes occurred when there was a high frequency of asynapsis during the first meiotic division. In this hybrid, approximately 39% of chromosomes were unpaired at metaphase I. Within the same cell at anaphase I, sister chromatids of univalents underwent precocious separation and formed laggard chromatids whereas paired chromosomes segregated without separation of sister chromatids as in normal meiosis. This asynchrony was frequently accompanied by incomplete or no movement of chromosomes toward the poles and restitution leading to unreduced chromosome constitutions. Reductional meiosis was restored in progeny where asynapsis frequencies were low. Two progeny plants with approximately 5 and 7% of unpaired chromosomes at metaphase I showed full restoration of reductional meiosis. Conclusions The study revealed that formation of 2n gametes occurred when asynapsis (univalent) frequency at meiosis I was high, and that normal gamete production was restored in the next generation when asynapsis frequencies were low. Asynapsis-dependent 2n gamete formation, previously supported by evidence largely from wheat and its relatives and grasshopper, is also applicable to hybrids from the dicotyledonous plant genus Trifolium. The present results align well with those from these widely divergent organisms and strongly suggest common molecular mechanisms involved in unreduced gamete formation.

Studies on Basic Chromosome Number, Ploidy Level, Chromosomal Association and Configuration and Meiotic Behavior in Mulberry (Morus Spp.)

Mulberry leaves are primary food for silkworm, Bombyx mori L. to feed silkworms and harvest quality silk cocoons. Mulberry belongs to family Moraceae and includes 60 species found distributed in both Hemisphere. In mulberry, chromosome numbers are varies from 2n = 28 to 22n = 308 (Diploid to Decosoploid) with ploidy level x to 22x. Based on chromosome numbers and meiotic behaviors x = 14 has been considered as basic chromosome numbers of the genus. In the present study, two diploids, two uneuploids, two triploids and two teteraploids mulberry varieties were selected for detailed chromosomal numbers and meiotic behaviors belongs to three species, namely Morus indica, Morus alba and Morus latifolia. Varieties, Vishaala and Kosen were diploids with 2n = 2x = 28 chromosomes and varieties Ber-S1 and S13 were uneuploids with 2n = 30 chromosomes belongs Morus indica. Varieties NAO Khurkul and KPG-1 were triploids with 2n = 3x = 42 chromosomes belongs to Moru alba and varieties Kokuso and Icheihei were tetraploids with 2n = 4x = 56 chromosomes. Diploids and uneuploids were showed normal meiosis with high pollen fertility and triploids and teteraploids were showed abnormal meiosis with low pollen fertility, due to virtue of higher ploidy level have been discussed in this chapter.

A SUBTILISIN-LIKE SERINE PROTEASE1 (OsSUBSrP1), plays an important role in the wax and cutin pathway, is essential for panicle development in rice

Panicle degeneration is a severe physiological defect and causes reduction in grain yield. In this study, we characterized and presented the functional analysis of our previously reported mutant apa1331 (apical panicle abortion1331) that showed apical spikelet degeneration. The anthers from the apical spikelets of apa1331 were degenerated, pollen-less and showed lack of cuticle formation. Transverse sections showed normal meiosis till stage 5-6, however, defects in post-meiotic microspore development were found at stage 8-9 in apa1331. Measurement of wax and cutin analysis showed a significant reduction in anthers of apa1331 compared to Wildtype (WT). Quantification of H2O2 and MDA has indicated the excessive ROS (reactive oxygen species) in apa1331. Trypan blue staining, and TUNEL assay revealed cell death and excessive DNA fragmentation in apa1331. Map-based cloning and Mutmap analysis identified a candidate gene (LOC_Os04g40720) that is a SUBTILISIN-LIKE SERINE PROTEASE (OsSUBSrP1) which harbored an SNP (A>G) in apa1331. CRISPR-mediated knock-out lines of OsSUBSrP1 displayed spikelet degeneration comparable to apa1331. Global gene expression analysis revealed a significant downregulation of wax and cutin biosynthesis genes e.g., OsWDA1, OsMS2 and OsCER4 in apa1331. Our study reports the novel role of SUBSrP1 in ROS-mediated cell death in panicle development.

Spastin interacts with CRMP5 to promote spindle organization in mouse oocytes by severing microtubules

Microtubule-severing protein (MTSP) is critical for the survival of both mitotic and postmitotic cells. However, the study of MTSP during meiosis of mammalian oocytes has not been reported. We found that spastin, a member of the MTSP family, was highly expressed in oocytes and aggregated in spindle microtubules. After knocking down spastin by specific siRNA, the spindle microtubule density of meiotic oocytes decreased significantly. When the oocytes were cultured in vitro, the oocytes lacking spastin showed an obvious maturation disorder. Considering the microtubule-severing activity of spastin, we speculate that spastin on spindles may increase the number of microtubule broken ends by severing the microtubules, therefore playing a nucleating role, promoting spindle assembly and ensuring normal meiosis. In addition, we found the colocalization and interaction of collapsin response mediator protein 5 (CRMP5) and spastin in oocytes. CRMP5 can provide structural support and promote microtubule aggregation, creating transportation routes, and can interact with spastin in the microtubule activity of nerve cells (30). Knocking down CRMP5 may lead to spindle abnormalities and developmental disorders in oocytes. Overexpression of spastin may reverse the abnormal phenotype caused by the deletion of CRMP5. In summary, our data support a model in which the interaction between spastin and CRMP5 promotes the assembly of spindle microtubules in oocytes by controlling microtubule dynamics, therefore ensuring normal meiosis.

Sex without crossing over in the yeastSaccharomycodes ludwigii

Meiotic recombination is a ubiquitous function of sexual reproduction throughout eukaryotes. Here we report that recombination is extremely suppressed during meiosis in the yeast speciesSaccharomycodes ludwigii. DNA double-strand break formation, processing and repair are required for normal meiosis but do not lead to crossing over. Although the species has retained an intact meiotic gene repertoire, genetic and population analyses suggest the exceptionally rare occurrence of meiotic crossovers. We propose thatSd. ludwigiihas followed a unique evolutionary trajectory that possibly derives fitness benefits from the combination of frequent fertilization within the meiotic tetrad with the absence of meiotic recombination.

The cohesin release factor Wapl interacts with Bub3 to govern SAC activity in female meiosis I

During mitotic prophase, cohesins are removed from chromosome arms by Wapl to ensure faithful sister chromatid separation. However, during female meiosis I, the resolution of chiasmata requires the proteolytic cleavage of cohesin subunit Rec8 along chromosome arms by Separase to separate homologs, and thus the role of Wapl remained unknown. Here, we report that Wapl functions as a regulator of spindle assembly checkpoint (SAC) to prevent aneuploidy in meiosis I. Depletion of Wapl accelerates meiotic progression, inactivates SAC, and causes meiotic defects such as aberrant spindle/chromosome structure and incorrect kinetochore-microtubule (K-MT) attachment, consequently leading to aneuploid eggs. Notably, we identify Bub3 as a binding partner of Wapl by immunoprecipitation and mass spectrometry analysis. We further determine that Wapl controls the SAC activity by maintaining Bub3 protein level and document that exogenous Bub3 restores the normal meiosis in Wapl-depleted oocytes. Together, our findings uncover unique, noncanonical roles for Wapl in mediating control of the SAC in female meiosis I.

Spastin Interacts with CRMP5 to Promote Spindle Organization of Mouse Oocytes by Severing Microtubules.

Background ： Microtubule-severing protein (MTSP) is highly critical for the survival of both mitotic and post-mitotic cells.However, the study of MTSP in the meiosis of mammalian oocyte has not been reported. Results ：We found that spastin, a member of the MTSP family, was highly expressed in oocyte and aggregated in spindle microtubules. After knocking down spastin by specific siRNA, the spindle microtubule density of meiotic oocyte decreased significantly. When the oocyte was cultured in vitro, the oocyte lacking spastin showed obvious maturation obstacles. Combining with the microtubule severing activity of spastin, we speculate that spastin on spindle may increase the microtubule broken ends by severing microtubules, thus playing a nucleating role, promoting spindle assembly and ensuring normal meiosis. In addition, we found that there was co-localization and interaction between CRMP5 and spastin in oocyte. The knockdown of CRMP5 may also lead to spindle abnormalities and developmental disorders in oocyte. Overexpression of spastin may save the abnormal phenotype caused by deletion of CRMP5. Conclusions ：To sum up, our data support a model in which the interaction between spastin and CRMP5 promotes the assembly of spindle microtubules in oocyte by controlling microtubule dynamics, thus ensuring normal meiosis.

Integration of metabolome and transcriptome reveals flavonoid accumulation in the intergeneric hybrid between Brassica rapa and Raphanus sativus

Brassica rapa and Raphanus sativus are two important edible vegetables that contain numerous nutritional ingredients. However, the agronomic traits and nutritional components of the intergeneric hybrid of B. rapa and R. sativus remain poorly understood. In this study, we used a stably inherited intergeneric hybrid of B. rapa and R. sativus as a model to study its metabolome and transcriptome profiles. Morphological and cytological analysis showed the intergeneric hybrid had the expected chromosome number and normal meiosis behavior. Moreover, the metabolome analysis showed multiple important secondary metabolites, including flavonoids and glucosinolates, were significantly upregulated in the hybrid. Furthermore, transcriptome data revealed that the expression level of the important genes involved in phenylpropanoid and flavonoid pathways was significantly upregulated in the hybrid. Ultimately, our data indicate the intergeneric hybrid will be a valuable bioengineering resource and promise to become a new-type hybrid vegetable with great medicinal value in future.

Analysis on the Meiosis-Related Gene (Dmc1, Ph1) Expression in Autotriploid Carassius auratus

Triploid is usually considered to be unable to perform normal meiosis due to the abnormal behavior of the three sets of chromosomes. But autotriploid Carassius auratus in the Dongting water system (3n = 150, abbreviated as 3nCC) can perform normal meiosis. In artificial autotriploid Carassius auratus (3n = 150, abbreviated as 3nRR), female individuals undergo normal meiosis and produce mature gametes, while male individuals cannot. To better understand the effects of triploidization on meiosis in fish, we study the structure, methylation level, and expression level of meiosis-related genes (Dmc1, Ph1) in diploid Carassius auratus (2n = 100, abbreviated as 2nCC), Carassius auratus red var.(2n = 100, abbreviated as RCC), 3nCC and 3nRR. The results show that, compared with their diploid ancestors (2nCC and RCC), Dmc1 and Ph1 genes are hypomethylated in all 3nCC and female 3nRR, while are hypermethylated in male 3nRR. Correspondingly, Dmc1 and Ph1 genes are highly expressed in all 3nCC and female 3nRR, while are lowly expressed in male 3nRR. These results indicate that high expression of meiosis-related genes can contribute to restoration of bivalent pairing during meiosis in autotriploid Carassius auratus. This study provides new insights into the effect of DNA methylation on the fertility in triploid fish.

The evolution of meiotic sex and its alternatives

Meiosis is an ancestral, highly conserved process in eukaryotic life cycles, and for all eukaryotes the shared component of sexual reproduction. The benefits and functions of meiosis, however, are still under discussion, especially considering the costs of meiotic sex. To get a novel view on this old problem, we filter out the most conserved elements of meiosis itself by reviewing the various modifications and alterations of modes of reproduction. Our rationale is that the indispensable steps of meiosis for viability of offspring would be maintained by strong selection, while dispensable steps would be variable. We review evolutionary origin and processes in normal meiosis, restitutional meiosis, polyploidization and the alterations of meiosis in forms of uniparental reproduction (apomixis, apomictic parthenogenesis, automixis, selfing) with a focus on plants and animals. This overview suggests that homologue pairing, double-strand break formation and homologous recombinational repair at prophase I are the least dispensable elements, and they are more likely optimized for repair of oxidative DNA damage rather than for recombination. Segregation, ploidy reduction and also a biparental genome contribution can be skipped for many generations. The evidence supports the theory that the primary function of meiosis is DNA restoration rather than recombination.